Generally laser communications and laser sensors require the ability to very rapidly scan (e.g. direct) the laser beam(s) over a wide angle, i.e. such as when the scanner is used in the transmit mode. In the receive mode, the scanner needs to be able to very rapidly direct incoming light from any particular angle selected from a wide variation of angles. In addition, for target or source acquisition, the receive mode should initially start out in a wide-angle/stationary search mode in which all optical elements in the scanner are each pointed at a different angle. Then when a signal is acquired, all the scan elements are pointed in an optimal direction corresponding to the signal. This latter mode (e.g. focused mode) is needed in laser communications to increase both security and signal to noise ratio.
Focusing of the scanner so that all the scan elements are pointed in the optimal direction is generally obtained by beam steering where many small laser beams are combined by stacking and/or by super-positioning the small laser beams. However, directing the resultant combined laser beam involves movement of a large mass, such as with a gimbaled mirror system or a sheet of a lenslet array that provides slow response times. Deformable mirrors may also be employed for beam steering where small angular deviations can be made with the deformable mirrors however, these deformable mirrors are unable to provide wide angle, two-dimensional sweeps of a large diameter laser beam without any obstructions. Other systems for beam steering can also be utilized in scanners such as, for example, Risley prism mechanisms, beam steering mechanisms manufactured by Metastable Instruments, Inc. of Peters, Mo., USA and micro-opto-electro-mechanical chips. Liquid crystals can also employed for beam steering but the response time for liquid crystal beam steering is approximately tenths of a second with a fairly large beam divergence (e.g. tens of degrees).
It would be advantageous to have a wide angle scanning system in which small/low mass scan optics allow for fast response times when focusing the scanner in a predetermined direction.